Filter Magnetograph Measurements at Meudon Observatory

International Astronomical Union Colloquium ◽

10.1017/s0252921100029092 ◽

1993 ◽

Vol 141 ◽

pp. 199-202

Author(s):

Audouin Dollfus ◽

Jacques Moity

Keyword(s):

Magnetic Field ◽

Transverse Magnetic Field ◽

Observational Studies ◽

Neutral Line ◽

Active Regions ◽

Transverse Magnetic ◽

Birefringent Filter ◽

Solar Active Regions

SummaryWe report observational studies of solar active regions n°6150 and n°6850 during cycle 22. Observations were carried out with a tunable monochromatic birefringent filter coupled with a line-shifter and a Stokesmeter as well as with a spectro-magnetograph, both at Meudon Observatory. AR n°6150 is typical of emerging flux regions, while AR n° 6850, with a complex preceding δ-spot, exhibits characteristic configurations of the transverse magnetic field for flaring activity: shear along the neutral line, and curvature coupled with anomalous Evershed mass motions.

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Radio Measurements of Coronal Magnetic Fields

International Astronomical Union Colloquium ◽

10.1017/s0252921100024933 ◽

1994 ◽

Vol 144 ◽

pp. 21-28 ◽

Cited By ~ 4

Author(s):

G. B. Gelfreikh

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Solar Corona ◽

Active Regions ◽

High Sensitivity ◽

Coronal Magnetic Field ◽

Transverse Magnetic ◽

Radio Sources ◽

Radio Waves ◽

Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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A Synthesized Method for Solving the 180° Ambiguity of Solar Transverse Magnetic Field

International Astronomical Union Colloquium ◽

10.1017/s0252921100029638 ◽

1993 ◽

Vol 141 ◽

pp. 461-464

Author(s):

Wang Huaning ◽

Lin Yuanzhang

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Transverse Magnetic Field ◽

Field Model ◽

Zeeman Effect ◽

Free Field ◽

Active Regions ◽

Transverse Magnetic ◽

Vector Magnetograms ◽

Divergence Equation

The 180° ambiguity of the transverse magnetic field measured by a heliomagnetograph is an intrinsic problem due to the linear polarization in Zeeman effect(Harvey, 1969). Thus we have to make use of some criteria for calibrating the transverse magnetic fields in vector magnetograms. Up to now, a few criteria have been suggested by some solar physicists (Harvey, 1969; Krall et al., 1982; Sakurai et al., 1985; Aly, 1989; Wu and Ai, 1990; Canfield et al., 1991. The existing criteria could be classified as observational criteria and mathematical criteria. The former is based on the observation facts, such as the fibrils and the filaments in solar filtergrams, and the latter is derived from the mathematical model of solar magnetic field, such as divergence equation (∆. B = 0), potential field model and force-free field model. These criteria, however, are not applicable to all solar active regions, especially to those with complicated magnetic fields. For this reason, we suggest a synthesized method for calibrating the transverse magnetic fields in solar vector magnetograms.

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